code: def test_central_longitude(lon):
      crs = ccrs.Mercator(central_longitude=lon)
      other_args = {
          "ellps=WGS84",
          f"lon_0={lon}",
          "x_0=0.0",
          "y_0=0.0",
          "units=m",
      }
      check_proj_params("merc", crs, other_args)
  
      assert_almost_equal(
          crs.boundary.bounds,
          [-20037508, -15496570, 20037508, 18764656],
          decimal=0,
      )
  
file_path: cartopy/lib/cartopy/tests/crs/test_mercator.py
imports: from numpy.testing import assert_almost_equal
  import pytest
  import cartopy.crs
  from .helpers import check_proj_params
label_desc: Use image node_id 4 for calling a global function with example usage: test_central_longitude(lon) without return types